The present invention relates to use of one or more flow through electrodes with automated calibration.
As used herein, the term xe2x80x9cflow through electrodexe2x80x9d includes electrodes used for measuring characteristics or constituents in aqueous solutions including pH, electrical conductivity, dissolved oxygen, specific ion(s) and combinations thereof. The term xe2x80x9cflow through electrodexe2x80x9d is interchangeable with the term xe2x80x9cinsertion electrodexe2x80x9d.
Flow through electrodes are used extensively for monitoring industrial processes as well as geochemical conditions of surface water and/or ground water. Operation of flow through electrodes or insertion electrodes always requires calibration to insure accurate measurements are collected from the sample aqueous solution. For periodic measurements or short term studies, manual calibration and measurement of the sample liquid is satisfactory. However, surface water and/or groundwater are extensively monitored at remote locations over long periods of time wherein manual calibration is so labor intensive and/or costly that it is scheduled infrequently and merely assumed to be correct between calibrations.
In FIG. 1 (prior art) an automated monitoring system 100 has a sample inlet 102 directed to at least one flow through electrode(s) 104 with an effluent or waste port 106. At least one computer 108 controls the sample flow and records data from the at least one flow through electrode(s) 104 for a liquid sample. In addition, it is known that a multi-port valve 110 may be used to introduce various liquid samples through the electrode(s) 104. Further, the sample inlet 102 may include a pump 111 for metering the sample. A disadvantage of these prior art systems 100 is the difficulty of calibration of the electrode(s) 104. For calibration, the entire monitoring system 100 must be removed from sample flow and the electrode(s) 104 manually disconnected from the tubing 112. The electrode(s) 104 is/are calibrated by exposure to calibration solutions. In addition to interrupting sampling, significant labor is required for calibration. For certain electrode(s) 104 sensitive to pressure and/or flow rate additional care (labor, time) is needed to match test conditions for an accurate calibration.
Thus, there is a need in the art of flow through electrode monitoring for an improved automated monitoring apparatus with an automated calibration capability.
The present invention is an improved automated flow through electrode liquid monitoring system. The automated system has a sample inlet to at least one flow through electrode with a waste port. At least one computer controls the sample pump and records data from the at least one flow through electrode for a liquid sample. The improvement relies upon
(a) at least one source of a calibration solution; connected to
(b) an injection valve connected to the sample inlet and connected to said calibration source, the injection valve further connected to the at least one flow through electrode, wherein the injection valve is controlled by the computer to select between the liquid sample or the calibration sample.
Advantages include diverting sample flow rather than interrupting sample flow, improved accuracy because of more frequent calibrations, capability of matching test conditions of flow rate and/or pressure, capability of multi-point calibrations, no additional labor for calibration, and no need to remove the flow through electrode(s) for calibration.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.